Drew Brees is hurting like hell today ... medical tests on the New Orleans Saints QB reportedly revealed he's dealing with multiple rib fractures and a collapsed lung.
The 41-year-old was forced to leave Sunday's win over the 49ers after he took a huge hit in the 2nd quarter ... and ESPN's Ed Werder says X-rays Monday showed the dude's ribs are jacked up.
Brees suffered 2 fractured ribs and a collapsed lung thanks to the hard tackle by Kentavius Street, Werder reports.
Werder added doctors also discovered Brees had 3 other fractured ribs from a hit he took against Tampa Bay on Nov.